Delta's New 717

PeanuckleCRJ said:
Unless limitation restricted, derating climb thrust burns more gas than climbing at max climb. Bad idea out of ATL.
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How? It's a 15% or 20% reduction in engine power which equals a similar reduction in fuel flow. I doubt the difference in time to top of climb and start of cruise burn is enough to cancel out the reduced fuel flow all the way up.
 
BobDDuck said:
How? It's a 15% or 20% reduction in engine power which equals a similar reduction in fuel flow. I doubt the difference in time to top of climb and start of cruise burn is enough to cancel out the reduced fuel flow all the way up.
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It is at least that in reduction in climb and acceleration rate... certainly more burn than an unrestricted climb. Think about the exponential component of thrust capability of engines...
 
I don't buy it.

Next time I work a longer leg (and by longer I mean more than 20 minutes) I pull the performance manuals and find the difference in time to TOC with a derate vs a LIM climb. And also if it shows the fuel savings using derates.
 
BobDDuck said:
I don't buy it.

Next time I work a longer leg (and by longer I mean more than 20 minutes) I pull the performance manuals and find the difference in time to TOC with a derate vs a LIM climb. And also if it shows the fuel savings using derates.
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Please do. The legs in HI are a far different animal for a 20 minute interisland leg. Those would certainly be appropriate to derate climb power.

Derg needs to derate his climb power on his A330 by 20% to save gas PDX-NRT..... (hint hint)
 
PeanuckleCRJ said:
Unless limitation restricted, derating climb thrust burns more gas than climbing at max climb. Bad idea most of the time, and particularly out of ATL.
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It's not about fuel. It does burn just a tad bit more fuel, but the reduction in maintenance costs on the engines far exceeds the extra fuel burn. If the power remains at CLB-1 for the first 10 minutes of the flight, there is a huge reduction in power-by-hour costs.
 
BobDDuck said:
I don't buy it.

Next time I work a longer leg (and by longer I mean more than 20 minutes) I pull the performance manuals and find the difference in time to TOC with a derate vs a LIM climb. And also if it shows the fuel savings using derates.
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While we can't derate our climb thrust, we'll climb at Mach .60 in the XR in order to get to cruise altitude quicker, where we'll burn less gas. The numbers can be stark on long legs if you don't stick to it.
 
jtrain609 said:
While we can't derate our climb thrust, we'll climb at Mach .60 in the XR in order to get to cruise altitude quicker, where we'll burn less gas. The numbers can be stark on long legs if you don't stick to it.
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Mach .60 with your hair on fire!
 
jtrain609 said:
Unless you're talking about turkeys and Pinchanickle is discussing fine German automobiles, I'm not sure how.
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Allow my inner engineer to come out for a second...

(Climb speed to TOC : Fuel Savings) != (Climb Thrust to TOC : Fuel Savings)
 
Interesting.

Way different motor, butGE asked us to run either full climb or one climb de- rate, not the 2nd climb de- rate as it's hard on the fuel nozzles. Don't ask me why, but the guy said so & that engine is his life. De- Rate is washed out by 15k anyway.

On our jet, taking off with flaps 20 and not accelerating until 3000' MSL vs flaps 10 accelerating at 1000' (lots of variables - so if you're not familiar just trust me) can soak up the 15% fuel saving between a -400 and a 74 Classic. In as much, a flight idle descent with a flaps 25 landing compared to a flaps 30 landing with a small level segment can offset the fuel savings over a 9+ hour flight - probably one ton extra fuel.
 
BobDDuck said:
Allow my inner engineer to come out for a second...

(Climb speed to TOC : Fuel Savings) != (Climb Thrust to TOC : Fuel Savings)
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Aren't they both manners of saving fuel? I'm not trying to be obtuse, I'm just not understanding what you're saying.
 
Polar742 said:
Interesting.

Way different motor, butGE asked us to run either full climb or one climb de- rate, not the 2nd climb de- rate as it's hard on the fuel nozzles. Don't ask me why, but the guy said so & that engine is his life. De- Rate is washed out by 15k anyway.
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We went back and forth during the fuel spike in 2008. When the spike went all the way up to $140/bbl, we were back to full rated thrust for climb, because the higher fuel prices soaked up all of the savings on maintenance. But once the price dropped down below $120/bbl again, we were back to the de-rate. We always worked with Boeing engineers to get the best numbers. It's the same reason we encourage the use of automation (or at least did before the Tex-ass people came around). Boeing engineers said that using the autopilot during the climb saved 1% in fuel burn. I wish our new masters paid such close attention to saving money without compromising safety, but it seems like we flush it down the toilet now instead.
 
jtrain609 said:
Aren't they both manners of saving fuel? I'm not trying to be obtuse, I'm just not understanding what you're saying.
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Climbing at a slow airspeed, but still using max climb gets you up to altitude faster where you can cruise and save gas. So your fuel savings are derived from the longer cruise segment.

Climbing at normal airspeed but using reduced power takes longer to get you up to cruise. However, you are saving gas (and engine wear) the whole way up using a reduced power settings. The question becomes, which saves more gas? The reduced power climb or the extra time you'll spend at cruise if you get there fast. Obviously there are a ton of variables but I'm of the opinion that the amount of fuel saved climbing out with the power reduced is greater than the amount of fuel saved during the delta in cruise time between TOC at max climb power and TOC in reduced climb power.

Picture for the visual people (and because I'm bored):

fuel_zps1b1d2d0d.png


B+C should burn less than A+D.
 
Duck, according to Boeing (at least on the plane that you and I fly), the plane burns more fuel using derated climb power. It burns more fuel using FLEX power for takeoff, also. The savings is purely in engine wear, not in fuel burn.
 
ATN_Pilot said:
Duck, according to Boeing (at least on the plane that you and I fly), the plane burns more fuel using derated climb power. It burns more fuel using FLEX power for takeoff, also. The savings is purely in engine wear, not in fuel burn.
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I know about the flex having a higher fuel burn, but the data sheet I have shows a reduction in fuel (of course it doesn't say how much) for a CLB2 and CLB1 setting. That said, our information and tech data is lacking in just about every other way so I wouldn't be surprised if this was wrong too.
 
Interesting. We're told that our data came directly from Boeing engineering, so it's probably trustworthy. Of course, they never showed us the raw data, just gave us information about it, so hard telling.
 
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